Transistor carrier multiplex equipments. I. Broad design and salient circuit features

Basic principles are described of a 960-channel carrier system developed jointly by the Standard Telephone and Cables Ltd., Standard Elektric Lorenz. (Germany) and Bell Telephone Manufacturing Company (Belgium). Double modulation version translates pre-groups of three channels each into 12-24 kc/s band and then shifts them to form a 60-108 kc/s group. Single modulation version is based on crystal filters. Out-of-band signalling frequency is 3825 c/s. Very large terminal installation have a 2480 kc/s master oscillator with AT crystal vibrating on its fifth overtone; smaller installations employ a 124 kc/s master oscillator with a relatively simple crystal oven and simple oven temperature control. Basic frequencies are generated by dividing 124 kc/s down to 4 kc/s in a five-stage counter. Saturated core transformers are used for enhanced harmonic generation at lower frequencies, and supergroup carriers are generated from highly symmetrical 124 kc/s pulses. Both germanium and silicon transistors are employed, and extensive use is made of ferrite pot-cores for inductors.